KT-64385 Enable K2 KAPT by default

Also adds support for front-end compiler plugins in Kapt

compiler/cli/cli-common/gen/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArgumentsCopyGenerated.kt

@@ -78,7 +78,6 @@ fun copyK2JVMCompilerArguments(from: K2JVMCompilerArguments, to: K2JVMCompilerAr
     to.typeEnhancementImprovementsInStrictMode = from.typeEnhancementImprovementsInStrictMode
     to.useFastJarFileSystem = from.useFastJarFileSystem
     to.useJavac = from.useJavac
-    to.useKapt4 = from.useKapt4
     to.useOldBackend = from.useOldBackend
     to.useOldClassFilesReading = from.useOldClassFilesReading
     to.useOldInlineClassesManglingScheme = from.useOldInlineClassesManglingScheme

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.kt

@@ -845,16 +845,6 @@ This option is deprecated and will be deleted in future versions."""
             field = value
         }
 
-    @Argument(
-        value = "-Xuse-kapt4",
-        description = "Enable the experimental KAPT 4."
-    )
-    var useKapt4 = false
-        set(value) {
-            checkFrozen()
-            field = value
-        }
-
     override fun configureAnalysisFlags(collector: MessageCollector, languageVersion: LanguageVersion): MutableMap<AnalysisFlag<*>, Any> {
         val result = super.configureAnalysisFlags(collector, languageVersion)
         result[JvmAnalysisFlags.strictMetadataVersionSemantics] = strictMetadataVersionSemantics

compiler/cli/src/org/jetbrains/kotlin/cli/common/arguments.kt

@@ -8,7 +8,6 @@ package org.jetbrains.kotlin.cli.common
 import com.intellij.ide.highlighter.JavaFileType
 import org.jetbrains.kotlin.cli.common.arguments.CommonCompilerArguments
 import org.jetbrains.kotlin.cli.common.arguments.CommonToolArguments
-import org.jetbrains.kotlin.cli.common.arguments.K2JVMCompilerArguments
 import org.jetbrains.kotlin.cli.common.arguments.ManualLanguageFeatureSetting
 import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity
 import org.jetbrains.kotlin.cli.common.messages.MessageCollector
@@ -48,7 +47,6 @@ fun CompilerConfiguration.setupCommonArguments(
         }
     }
 
-    switchToFallbackModeIfNecessary(arguments, messageCollector)
     setupLanguageVersionSettings(arguments)
 
     val usesK2 = arguments.useK2 || languageVersionSettings.languageVersion.usesK2
@@ -57,34 +55,6 @@ fun CompilerConfiguration.setupCommonArguments(
     buildHmppModuleStructure(arguments)?.let { put(CommonConfigurationKeys.HMPP_MODULE_STRUCTURE, it) }
 }
 
-private fun switchToFallbackModeIfNecessary(arguments: CommonCompilerArguments, messageCollector: MessageCollector) {
-    fun warn(message: String) {
-        if (!arguments.suppressVersionWarnings) messageCollector.report(CompilerMessageSeverity.STRONG_WARNING, message)
-    }
-
-    if (arguments !is K2JVMCompilerArguments) return
-    val isK2 =
-        arguments.useK2 || (arguments.languageVersion?.startsWith('2') ?: (LanguageVersion.LATEST_STABLE >= LanguageVersion.KOTLIN_2_0))
-    val isKaptUsed = arguments.pluginOptions?.any { it.startsWith("plugin:org.jetbrains.kotlin.kapt3") } == true
-    when {
-        isK2 && isKaptUsed && !arguments.useKapt4 -> {
-            warn("Kapt currently doesn't support language version 2.0+. Falling back to 1.9.")
-            arguments.languageVersion = LanguageVersion.KOTLIN_1_9.versionString
-            if (arguments.apiVersion?.startsWith("2") == true) {
-                arguments.apiVersion = ApiVersion.KOTLIN_1_9.versionString
-            }
-            arguments.useK2 = false
-            arguments.skipMetadataVersionCheck = true
-            arguments.skipPrereleaseCheck = true
-            arguments.allowUnstableDependencies = true
-        }
-        arguments.useKapt4 -> warn(
-            if (isK2) "K2 kapt is an experimental feature. Use with caution."
-            else "-Xuse-kapt4 flag can be only used with language version 2.0+."
-        )
-    }
-}
-
 fun CompilerConfiguration.setupLanguageVersionSettings(arguments: CommonCompilerArguments) {
     languageVersionSettings = arguments.toLanguageVersionSettings(getNotNull(CLIConfigurationKeys.MESSAGE_COLLECTOR_KEY))
 }